Titaniferous material for producing titanium dioxide



July 9, 1949. w. M. PEIRCE El'AL 2,476,453

I'ITANIFEROUS MATERIAL FOR PRODUCING TITANIUM DIOXIDE Filed Aug. 19,1947 FIG I 0.8 0.9 L0 Ll L2 L3 L4 L5 INVENTORS 66 7O 74 78 82 WILLIS M.PEIRCE,

ROBERT K. WARING mo LUTHER D. FETTEROLF BY (LMCRJSI a-Maws ATTORNEYStm'raanir. FOR PRODUClNG 1'. DIOXIDE Willis M. Peirce, Leliigliton, andRobert K. Waring and Luther DrFctterolf, Palmerton, Pa", assignors, bymesn'e assignments, to Quebec Iron and Titanium Corporation, New York,N. 2., a corporation of Delaware Application August 19, 1947, Serial No.769,470

This invention relates to titaniferous material for producing titaniumdioxidaand more particularly to titanium slag concentrates suitable forchemical processing to produce pigment titanium dioxide. The principalobjector the invention is the provision, as a new article of commerce,of atitanium slag concentrate of good quality for the production oftitanium dioxide plgment by thesulfuric acid digestion process, and witha titanium-iron ratio so high that ferrous sulfate need not be removedby crystallization in the course of the pigment production process. v

-There exist inseveral parts of the world large deposits of orescomposed largely of the oxides 4 CBS. (Ci. 75-30) found thattitanium-iron ores can be smelted under properly controlled conditionsof charge composition with relatively little and even no added flux toproduce a. titanium slag concentrate meeting these specifications and atthe same time producing a metallic iron product which can be marketed aspig iron.

of titanium and iron, with titanium present in in too low a percentagefor economic processing for the recovery of pigment titanium dioxide(T102) Numerous efforts have been made to recover either the iron or thetitanium from such ores, with indifferent and economically unsuccessfulresults. The treatment of such ores by conventional -smelting methods toproduce marketable pig iron has failed because of the adverse effect ofthe titanium on the behavior of the slag produced. Very little seriousconsideration has heretofore been given to the possibility of treating'these ores with the primary object of recovering the titanium ratherthan accepting its presence as a necessary evil.

Inthe endeavor to. produce a titanium slag concentrate by the smeltingof titanium-iron ores, we have found that the slag produced byconventional smelting practices is unsuitable for acid digestionand'leaching to produce a leach solution from which titanium hydrate(hydrated titanium dioxide) can be economically recovered by hydrolysis.It has heretofore been commonly supposed that substantial quantities offluxes, such for example as lime, soda and alumina; must be used insmelting titanium-iron ores in order to obtain slags of sufllcientfluidity to permit good separation of the metallic iron and slag andfree-tapping of the slag from the furnace. Where it is desired torecover the titanium, the use of such substantial quantities of fluxesis objectionable because the fluxes dilute and lower the titaniumcontent of the slag and render it uneconomical for pigment production.In an exhaustive investigation of the subject. we have determined thespecifications of the titanium slag concentrate required for subsequentsatisfactory and economical processing for the production of titaniumdioxide pigment by the conventional acid and equivalent processes. wehave also Thepresent invention contemplates the provision of a titaniumslag concentrate possessing the characteristics which we have found tobe required for subsequent satisfactory and economical chemicalprocessing. One characteristic of the slag is its high titanium grade,containing at least (and preferably at least 7.0%) titanium calculatedas T102. Another characteristic of the slag is its good digestingproperties under customary commercial conditions of acid digestion andleaching. Upon acid digestion and leaching of the slag, the recovery oftitanium in the leach solution is at least and preferably at least(usually referred to as the acid-to-titanium ratio") in the leachsolution of between 1.8 and 2.3. Additionally, the slag concentrate ischaracterized by a relatively high titanium to iron ratio as comparedwith the titaniferous concentrates heretofore customarily used in theproduction of pigment titanium dioxide by the conventional sulfuric aciddigestion process. As a result, pigment may be produced directly fromthe leach solution obtained by sulfuric acid digestion of the slagconcentrate without the necessity of removing part-of the iron in thesolution by crystallization in the form of copperas, as is the practicewhen using ilmenite ore concentrates. A further characteristicof theslag concentrate is that it is not highly reduced, although part of itstitanium content may be present in the form of oxides lower than Ti02,which lower oxides are herein collectively referred to as trivalenttitanuim. The amount of iron in the slag is generally indicative of theamount of trivalent titanium in the slag, the lower the iron content thegreater the trivalent titanium content. With an iron (Fe) content of 2to 20% and preferably 4 to 15% (present in the slag as FeO), the slaggenerally contains'a sufliciently low amount of trivalent titanium. Thedegree of reduction of the slag may be determined by heating it in airat a temperature of 800-1000 C. and determinwith an acid-to-titaniumdioxide ratiotent. With a slag of the contemplated low trivalenttitanium content, from 1 to 30%, and preferably not more than about ofthe titanium in the leachsolution will be present in the-form oftrivalent titanium.

The principal raw material source of titanium for the manufacture oftitanium dioxide pigment has heretofore been ilmenite ore, a ferrous t1-tanate, containing roughly about equal. parts of tianium dioxide andiron oxides with relatively small amounts of other oxides. In thechemical processing of ilmenite, or other suitable titaniferousmaterial, for the production of titanium dioxide pigment, thetitaniferous material is digested with acid, usually sulfuric acid, andthe digested (e. g. sulfated) mass is leached with water to obtain asolution of the resulting water-soluble salts (e. g. titanium and ironsulfates). Present day commercial practice for the digestion of ilmeniteinvolves an essentially autogenous method in which the heat of reactionbetween sulfuric acid and the ore is relied upon to maintain theelevated temperature required for complete reaction and to produce areadily leachable dry cake of titanium sulfate. The ore, ground so thatapproximately 90% passes a 325- mesh screen, is mixed with the requiredamount of sulfuric acid, usually of about 92-94% strength,

, in a suitable tank (a commercial digester may hold as much as tons ofilmenite). The wellmixed ore and acid is then heated to a temperature inthe range of 120-450 C., depending upon the particular ore being used,by introducing live steam into the bottom of the tank. Superficialreaction of ore and acid during the heating up period also supplies someheat. When the mass reaches the 120-150 C, temperature, a small amountof water is introduced into the tank so as to cause localized heatingthrough dilution of the acid. Vigorous reaction of the entire mass takesplace with the generation of sufllcient heat to complete the reactionand evaporate essentially all of the associated water, so that a drycake is produced in a matter of afew minutes. During the period ofviolent reaction, air is passed through the mass so that the resultingcake will be porous and therefore more amenable to leaching. Thereacting mass may reach a temperature of 175-200 C.-,' and during theseveral hours required for it to cool, additional baking takes placewhich aids in completingthe reaction and improving the recovery. Afterthe digested cake has cooled, leaching of the soluble titanium sulfateis carried out in the same tank.

In digesting and leaching the titanium ore, it is necessary not only toobtain a reasonable recovery of the titanium, but also to end up with atitanium sulfate solution having suitable properties for producing insubsequent processing a pigment grade titanium dioxide. Economic andtechnical considerations limit the amount of acid which should be usedfor digesting. If an excessive quantity of acid is required to obtain areasonable recovery of titanium, the cost of producing the pigment isincreased, because of the initial cost of the additional acid requiredper pound of titanium dioxide manufactured and the additional costassociated with the disposal of the greater quantity of waste acid.Furthermore, while a good recovery may be possible with a large excessof acid, the resulting solution is not suitable for pigment manufacture.The primary properties determining the suitability of the leach solutionfor pigment manufacture are (1) the concentration of titanium. (2) theacidto-titanium ratio, and (3) its stability. A titanium concentrationin the solution of about 200-250 grams of titanium dioxide per liter ispreferred, and it is desirable to approach closely this range ofconcentration directly in the leaching step so as to reduce to a minimumthe amount of evaporating that must be done to obtain the desired finaltitanium concentration. The ratio of the sulfuric acid content of thesolution to its titanium dioxide content should fall within the range of1.8 to 2.3. If the ratio falls below 1.8, unstable solutions are likelyto result and premature hydrolysis may take place. The stability of thesolution should be such as not to hydrolyze too readily, otherwisedifficulty may be experienced in handling it up to the precipitationstep. If the acid-to-titanium ratio exceeds 2.3, the rate of hydrolysisbecomes too slow and complete precipitation of the titanium will not bereadily realized, and the crude titanium hydrate formed will be coarseand aggregated and cannot be mufiled to a pigment of the best quality.

In calculating and expressing the acid-to-ti tanium ratio, the acid isdetermined by titration with sodium hydroxide and methyl orangeindicator. Thus, ml. (milliliter) of 10% barium chloride solution isplaced in a 400 ml. beaker, and 2 drops of methyl orange indicator isadded. -1 ml. of the solution to be tested is washed into the bariumchloride solution, and the volume is made up to 200 ml. with boilingwater. Titration, with good agitation, is carried out to a peach coloredend point with N/lO sodium hydroxide solution. By this method oftitration, the sulfate (S04) combined as titanium sulfate and freesulfuric acid is determined,'and expressed as grams of sulfuric acid(H2304) per liter of solution. The titanium is determined by 4 analysis,and expressed as grams of TiOz per liter of solution. These gram"determinations of sulfuric acid and titanium dioxide, per liter,

give the acid-to-titanium ratio of the solution.

The titanium slag concentrate of the invention can be processed for themanufacture of pigment titanium dioxide in much the same manner thatilmenite is now processed. It is high grade, at least and preferably atleast TiOz. At least and preferably at least of its 50 titanium contentis recoverable by customary methods of digestion and leaching with anacidto-titanium ratio in the leach solution of between 1.8 and 2.3. Inevaluating the digestibility of a slag, we use the following procedurewhich closely 55 simulates the conditions and results of the customarycommercial practice. About 6.5 pounds of the ground slag and about 13pounds of 93% sulfuric acid are mixed in a heated test pan (16 incheslong, 10 inches wide, and 9 inches high, 0 made of sheet iron). The panis'heated on a hot plate to initiate the reaction (in place of livesteam) and to compensate for the large radiation losses that wouldotherwise permit the mass to cool in much less time than in commercialscale 65 equipment. The exact amount and concentration of acid arevariables that affect the recovery. The mixture is stirred by hand withan iron hoe, and cc. of water is added when the mass has been heated tothe desired temperature (-175" 70 0. depending on the type of charge,concentration of acid etc); The stirring is continued during the violentreaction (which frequently starts without the addition of water) anduntil the mass hasdried up (generally about}; minutes), A 75 cover isplaced on the pan and it is allowed tosit on the hot plate at atemperature of around- 160 C. for two hours. When the digested mass iscool, it is chipped out of the pan, leached with cold water, filteredand analyzed. Slags of the invention, when digested and leached by thisprocedure, give a recovery of at least 80% of the titanium content withan acid-to-titanium ratio of 1.8 to 2.3 in a leach solution containing,by direct leaching, about 200-250 grams per liter of titanimn calculatedas TiOz. When slags of the invention are subjected todigestion andleaching in equipment of commercial size, the time required to secureequal or better recovery (conversion to titanium sulfate solution) ismuch less than that required for the treatment of ilmenite in the sameequipment and under the same conditions; in some cases the time requiredbeing only about half that required to effect the same results withilmenite.

When the titanium sulfate solution (prepared for hydrolysis) containsany iron sulfate (as is always the case in processing ilmenite and mostother titaniferous materials) a trivalent titanium content of 0.5 to 1%(based on the titanium in solution) is desired, since under thiscondition all iron present in the solution will be in the ferrous state.It is necessary that all iron in the solution be kept in the ferrousstate during hydrolysis and subsequent processing of the titaniumhydrate because ferric iron is much more readily adsorbed by the hydratethan is ferrous iron, and if ferric iron is present a pigment of goodquality cannot be obtained. If the trivalent titanium in the solutionexceeds about 1% of the total solubilized titanium, the excess trivalenttitanium should be oxidized before subsequent processing because of theadverse effect of the excess reduced titanium on pigment quality and topermit recovery of the titanium as titanium dioxide. Such excesstrivalent titanium may be oxidized by aeration in the presence of acopper catalyst, or in any other appropriate manner.

The titanium slag concentrate of the invention a is advantageously madeby a method which involves smelting, preferably in an electric arcfurnace, a charge mix made up of the titaniumiron ore, coal and flux(including such as is naturally present in the ore), the titanium, iron,coal and flux in the charge mix being correlated to produce, preferablywith a smelting temperature between 1500 and 1700 C., a metallic ironproduct (e. g. pig iron) and the titanium slag concentrate. The requiredhigh titanium grade of the slag is attained by limiting the amount offlux, and particularly added lime, in the charge mix, the amount ofadded lime not exceeding 10 parts by weight (and preferably notexceeding 6 parts) per 100 parts of ore, and varying from that maximumamount down to none at all. Coal or equivalent carbonaceous reducingagent is required in the charge mix for the reduction of the iron oxideto metallic iron and for carburizing the iron, but contrary toconventional smelting practice an excess of coal is avoided. The amountof coal included in the charge mix is slightly less than thattheoretically required to reduce the iron oxide in the ore (withoxidation of the carbon to carbon monoxide) and to carburize the iron.In general, this amount of coal will range from 8 to 14 parts by weightper 100 parts of ore. Coal is herein used generically to include cokeand any other carbonaceous materialsuitable as a reducing agent inmetallurgical smelting.

The ores which are particularly applicable to the production of the slagconcentrate of the invention are those falling within the followingcompositional ranges:

The gangue constituents in these ores are for the most part lime (CaO),magnesia (MgO) alumina (A1203) and silica (S102) Whatever iron in theform of ferrous oxide '(F'eO) is allowed, under the controlledconditions of smelting, to go into the slag acts in the nature of aflux,and the slag is formed of such iron, the gangue constituents of the oreand the ash of the coal, practically all of the titanium dioxide in theore, and such small amount of added flux as may be used. It isdesirable, in the smelting practice, to hold extraneous additions to aminimum and to produce as high grade titanium slag concentrate aspracticable.

For purposes of illustration, the invention will be particularlydescribed in conjunction with the smelting of Coulombepre of which thefollowing is a typical analysis:

Since slags of the invention contain at least TiOz, the remaining slagconstituents amount to 40% or less. The gangue constituents of Coulombeore account for about 20% of the remaining slag constituents, of whichabout 1% is CaO. The balance, i. e. 20% or less, of the slag is made upof ferrous oxide, or lime, or both. For reasons hereinafter explainedthe slag contains at least 2% iron (calculated as Fe but present in theslag as FeO). Depending mainly upon the composition of the charge, theslags may be high iron and low lime or high lime and low iron. Thus,slags containing 60% T102 may contain from 15 to 4.6% Fe and from 1 to15% CaO, and slags containing 70% T102 may contain from 7.7 to 2% ironand 1 to 8.4% CaO (1% CaO being derived from the gangue) in the case ofCoulombe ore. In the customary digesting and leaching practices,practically all of the slag, except its lime and silica contents aredissolved. Therefore, the more lime the slag contains the greater is theinsoluble residue. In present day plants designed for treating ilmenitelimited equipment for hand-ling insoluble residues is provided, sincethe amount of such residues is small (say 1% of the solution). In suchplants, the high-iron and low lime slags of the invention are preferred.On the other hand, the disposal of ferrous sulfate is troublesome, andin plants provided with appropriate equipment for handling solidresidues, the high lime and low iron slag may be preferred.

The amount of coal included in the charge mix is slightly less(generally about 10% less) than the theoretical amount required toreduce the iron oxide in the ore to metallic iron with oxidation ofcarbon-to carbon monoxide and to carburize the metallic iron product,which may contain from 1 to 3% carbon. The actual weight of coalincluded in the charge mix will depend, of course, uponthe' grade of thecoal. that is, its

' 1? available carbon content. A high grade coal is desirable, since theash content of the coal enters and hence dilutes. the slag. Throughoutthis specification, where weights or' parts of coal are specified, thecoal is a high grade anthracite containing about 13% ash, analyzing 60%$102, 30% A120: and Fat). In general, ores containing 30-35% ironrequire from 8 to 10 parts by'weight by weight of coal per 100 parts ofore. and ores containing 35 45% iron require from 10 to 14 parts of coalper 100 parts of ore. With Coulombe ore about 11 parts of coal per 100parts of ore generally give satisfactory results. and with ores of theAllard Lake type with higher iron (44.4% Fe) about 14 parts of coal per100 parts of ore give good results. More coal can be initially toleratedin continuous operation than in batch operation until a surplus of coalbuilds up in the furnace, when the amount of coal in the charge mix iscut back to about the same as in batch operation.

The amount of lime included in the charge mix will depend upon theamount of iron oxide to be left in the slag and the amount and nature ofthe gangue constituents of the ore and the ash of the coal. Thefollowing calculated slag compositions are based on smelting Petit Pasore, with 14 parts of coal and the indicated parts of lime (calculatedas CaO but added to the charge mix in the form of limestone) per 100parts of ore. The ore analysis is as follows:

Per cent Fe 42.2 T101 36.4 CM) 0.02 MgO 2.2 A1503 2.0 $10: 1.5 P105 0.01Bal. .68

Parts of Goo added to charge mic: per 100 parts of ore ig sggggfig Low11-511 slsgs High iron slags Per- Per- Percent cent cent 65.0 10.0 15.019. 05 15.25 10.18 3.10 1.00 .31 3.93 4.22 4.52 4. as 4.88 5.23 4.03 4.01 5.3:; "T0? ""35 Filg excess over 100% is due to expression of lowervalence titanium 8S 1.

In the actual smelting of a calculated charge mixture, a slag may beobtained with a titanium content (expressed as T101) considerablygreater than the calculated percentage, because of the presence in theslag of lower oxides of titanium resulting from the reduction duringsmelting of some titanium dioxide. For example, the existence ofconsiderable Th0: in the slag may show 85% or more T102 when the slag isanalyzed and the titanium reported as T102. Slags of such high trivalenttitanium tenor are very refractory and cannot be readily melted insmelting. Several lower oxides of titanium may be present in the slag.TiaOs in the common run of slags and Th0: in highly reduced slags havebeen identified by X-ray analysis, and other lower oxides, such asT1101, TiO and possibly others, are known to exist and may be present inthe slag. For convenience, all lower oxides of titanium are collectivelyreferred to herein as trivalent titanium (T1203) since'any lower oxideor combination of lower oxides can be calculated to equivalent T1205 0nthe basis of oxygen deficiency for T102.

The object of the smelting operation is to produce pig iron and thetitanium slag concentrate of the invention with high titanium content.The slag produced in smelting must be suficiently fluid to flow readilyfrom the furnace and separate cleanly from the iron. If the ore werepure iron and titanium oxides and all the iron were reduced, leaving apure titanium dioxide slag, the slag would not havethe necessaryfluidity. Fluxes must therefore be present to produce a slag of therequisite fluidity. A slag made up of titanium dioxide, lime and ferrousoxide in suitable proportions to give the slag adequate fluidity wouldbe rendered too viscous if a considerable part of the titanium dioxidewere reduced to exides of lower valence. Nevertheless, to produce pigiron in the operation, it is necessary to have a reducing agent presentto reduce the ferrous oxide, and while ferrous oxide is more easilyreduced than titanium dioxide, conditions can exist in a smeltingfurnace which will result in the reduction of some of the titaniumdioxide. Such reduction may occur even though the amount of carbonpresent is less than enough to reduce all of the ferrous oxide. Theconditions which favor the reaction of part of the carbon with titaniumdioxide, even though it should theoretically be used up by the ferrousoxide present are (1) the existence in the furnace of a zone of hightemperature, (2) the presence at local points of more than enough carbonto satisfy the ferrous oxide present at those points, and (3) the lackof subsequent opportunity for reoxidation of the reduced titanium oxidesby unreduced ferrous oxide. Homogenizing currents in the slag tend toprevent the existence of the .aforementioned conditions favorable to thereduction of titanium dioxide, but in a viscous slag such currents arenegligible. The electric arc furnace, with its zones of very hightemperature in the arcs, offers favorable conditions for the reductionof titanium dioxide.

A harmful reduction of titanium dioxide in the smelting operation isprevented by so proportioning the constituents of the charge mix thatwhen the coal included in the charge has reduced as much ferrous oxideas it will, the resulting slag made up of oxides of titanium, ganguematerial. unreduced ferrous oxide and deliberately added lime will havethe requisite fluidity at a temperature of 1500 to 1700 C. If thetemperature at which the resulting slag would be suiliciently fluid(provided the titanium dioxide were not reduced to any large extent)exceeds 1700" (2., then excessive reduction of titanium dioxide willoccur and a still higher temperature will be necessary for slagfluidity, resulting in an excessive operating temperature or evenrendering the operation impossible. 0n the other hand, slags whichbecome fluid at atemperature much below 1500 C. tend to reach acompletely molten state before the carbon has reduced as much ferrousoxide as intended, and these slags containing an excessive amount offerrous oxide are very corrosive to the furnace refractories.

[when the smelting operation is practiced in an electric arc furnace, itis necessary to carefully control the amount of coal in the charge sothat molten state A is a titanium the charge has reached a completelythe desired amount of ferrous oxide will have been reduced. The amountof unreduced ferrous oxide left in the slag will be sufficient, inconjunction with the other slag-forming constituents included in thecharge, to give a slag of proper fluidity at a temperature between 1500by the time into the furnace in such a manner (e. g. by intermittentcharging at the sides) as to bring it up to the melting temperature at amoderate rate, thus permitting reduction of a substantial part of theferrous oxide before melting of the charge takes place. In the zones ofthe arcs the graphite electrodes furnish a continuous source of carbonand the temperature is adequate for reduction of titanium dioxide, andsome reduction of titanium dioxide will take place. Hence the slagshould be tapped from the furnace within a limited time after it iscompletely molten to avoid excessive reduction of the titanium dioxide.

' The influence of lime on smelting behavior is pronounced and its useso changes the smelting conditions that slag characteristics aremarkedly different, depending upon the proportion of lime (CaO) to oreused in the charge. Smelting behavior and slag characteristics are alsodependent upon the coal addition to the charge. Thus, 1 part of coal per100 parts of ore neutralizes in many respects the effect of the additionof 2 parts of lime. The explanation will develop in the discussion ofthe smelting data hereinafter presented.

As a preliminary to the presentation of that data, a discussion of thechemical and mineralogical constitution of slags is desirable as well asan explanation of slag specifications as fixed by slag processing forthe production of titanium dioxide pigment. The analyses of two types ofslag produced from an ore (Allard Lake) of relatively low gangue contentare given below. Slag slag concentrate of the invention resulting from asmelting charge to which 6.4 parts of lime (aslimestone) were added per100 parts of ore. Slag B is a slag resulting from a smelting operationof the same ore without'lime addition and with more coal included in thecharge, and is unsuitable for chemical processing to produce pigmenttitanium dioxide.

Slag A Slag B Per uni Per cent Ti expressed as TiO; 70 86 FeO 7 2 13 1 55. 5 4. 5 5 3 3. 5 Miscellaneous oxides i. 5 2

g p a 102.0 105.0 Per cent weight gain on oxidation oi slag sample 2. 05.0

The percentage weight gains of the slags result from oxidation uponshortyheat treatment in air at a temperature of 800 to 1000" C. Ferrousoxide (FeO) in the slag is converted to ferric oxide (F8203) andaccounts for a percentage weight gain equal to ,6 of the percent of Fe)in the slag. The percentage weight gains attributable to oxidation 'ofthe FeO in slags A and B are therefore 0.8 and 0.2%, respectively.Weight gains of 1.2 and 4.8% to oxidation of reduced or lower oxides oftitanium in slags A and B, respectively. Calculations show thatabout 85%of the titanium in are therefore attributable,

and 1700 C. The charge should be introduced slag B is present as TiaOsorthere is present a.

the presence of TiO: (rutile) in amount corresponding to the estimatedTiO-2Tl0z present in" the unoxidized slag and MgO-2Ti0z in amountcompatible with the mo content of the slag.

The amount of trivalent titanium present in the slag has an importanteffect on slag quality. Highly reduced slag, such as slag B, isunsuitable for titanium pigment production by the acid digestionprocess. While satisfactory pigment can be produced from slags of thistype, the leach recovery of T: is low and the trivalent titanium contentof the leach solution is unduly high.

In acid digestion and leaching of the slag, oxidation of trivalenttitanium takes place to some giving leach extent, being usuallyrelatively greater the higher the trivalent titanium content of theslag. Slags giving a weight gain of 0.1 to 2% attributable to oxidationof trivalent titanium are generally pre-'- ferred, although slags ofgood quality can be produced with such weight gains up to 3.5%. Slagsgiving leach solutions with 1 to of the soll1-. bilized titanium in theform of trivalent titanium are preferred, but under practical conditionsof commercial smelting in an electric arc furnace more highly reducedslags are often produced, solution with and even as highv as ofthesolubilized titanium in the form of trivalent titanium. The excess oftrivalent titanium in the leach solution may be oxidized in anyappropriate manner.

The correlation between smelting conditions, charge composition and slagcomposition required to produce titanium slag concentrates of theinvention will be better understood from the following discussion ofsmelting data, and the accompanying drawing, in which the curves ofFigs. 1 and 2 show the energy requirement and slag properties,respectively, plotted against charge composition.

Smelting was conducted as a batch operation in an electric arc furnaceof 100 kw, capacity. Batches of 200 pounds of Coulombe titanium-ironore, limestone and coal where charged to the hot furnace and smelted tothe point at which the molten products tapped represented 100%recovtective slag skull which is maintained on the side walls of thefurnace. Selection of tap recovery as an endpoint of smelting affords aconvenient basis and serves better than any other to show the influenceof charge composition on energy requirement, smelting behavior, slagcharacteristics, leaching recoveries, etc.

Fig. 1 of the drawing shows the energy requirement per pound of ore forcharges varying in coal byincrements of 1 part per 100 parts of ore andin lime by increments of 2 parts per 100 parts of ore. The relativedisplacements of the energy requirement curves for charges of differentlime contents show the potent fluxing eifect of lime. In quantitativeterms, two parts of lime so flux the charge and subsequently fluidizethe melt that 100% recovery of molten products is obtained with adecrease of 0.1 kilowatt-hour per pound of ore. The eil'ect of variationin coal is even more pronounced. In general, a decrease in coal by onepart in the region of theoretical coal requirement is accompanied by adecrease in energy of 0.1 kilowatt-hour per pound of ore. 'In terms 01'energy, the addition of two parts of lime is equivalent to the removalof one part of coal and vice versa.

In Fig. 2 of the drawing, companion curves show the relationship betweencharge composition and slag characteristics, the parts of coal and limeper 100 parts of ore being plotted against the titanium in the slagreported in percent TiO-z. Thus, the titanium grade of the slag isplotted against coal content of the charge mix for each of the severalfigure, in the four figure columns, shows the percent of iron (presentas ferrous oxide) in the slag, the 2nd figure shows the weight gain ofthe slag upon oxidation (corrected for Fe- FezOa and is indicative ofthe trivalent titanium" in the slag, the 3rd figure shows the leachingrecoveryof titanium, and the bottomflgure shows the percent ofsolubilized titanium present in the leach solution as trivalenttitanium. The acid-totitanium ratios of the leach solutions are given inthe following table:

Acid-titanium ratio of leach solution The grade of the slag varies withlime addition, the titanium content of the slag decreasing as the limeaddition is increased. Increasing the addition of coal produces a markedincrease in the grade of the slag, although a decrease in slag grademight be expected in view of the dilution efiect of the coal ash.Additional coal reduces more of the titanium to the trivalent form, andin the resulting more highly reduced slag the 'IiOz equivalent of thetitanium in the slag is relatively and even abnormally high.

A consideration of Fig. 2 of the drawing shows that only within arestricted area are slags produced of that quality required forsubsequent chemical processing, namely (1) reasonably high grade, (2)good leaching recovery, (3) low trivalent titanium in the leach solutionand (4) satisfactory acid-to-titanium ratio. These qualities ingbehavior of dam of the compositional field will be discussed.

lower oxides proceeds. The effect is very de- :idedly that of increasingslag viscosity, and a greatly increased temperature is required toluidize the slag for tap. The higher temperature lime additions. The top12 required for tap results in' titanium The desired slag recoverieswere obtained from charges less. However, trivalent titanium trivalenttitanium content because of the defrom the reducing non-homogeneous andis so because slag composition. intermingled mass of low FeO-high T1305melt and relatively high rial.

FeO-relatively low T1305 ma- Cat) and low in titanium grade as well asessentially free from trivalent titanium. All four factors combine toproduce a l' w melting, fluid slag. The rapid development of a veryfluid slag results tapped at 1450-1500 reduction of titanium dioxidedoes not occur. particularly inasmuch as the high slag fluidity as- 2into line with the lower por-.

C., at which temperature 1 greater fluidity.

two series of runs I and aa'qacas 13 sures an equilibrium presumablyunfavorable to the co-existence of FeO and TiaOs.

The pronounced effect of small changes in lime is shown by the orderlysequence of slag values in progression from 10 C210 to 09.0.

The foregoing detailed discussion of the relationship between chargecomposition, smelting behavior, and slag quality has been entered intoin order to show the great importance of charge composition.Fortunately, the smelting process is not subject to such data appear toimpose. The results are believed to apply to a straight batch smeltingprocess and are probably qualitatively true for any process. However,the low rate of power input into the mil-kilowatt furnace heats up thecharge relatively slowly and there is every opportunity for ironreduction before fusion. Melting of the charge becomes increasinglydifficult as FeO becomes unavailable as a flux. At a higher power inputrate, the rate of temperature increase is more rapid and less time isavailable for iron serious limitations as the The charge mix was introdat 10 to 80 minute intervals. In the first run the charge was introducedthrough the roof 0 to the banks along the side walls. In the other rsfthe charge was thrown through the end doors upon the side-wall banks.

compared with batch smelting:

1. Cold charge on the bath holds down the slag temperature in theelectrode zone with the result that reduction of iron and titanium doesnot become excessive.

2. Some unreduced ore almost immediately enters the slag, therebymaintaining FeO as a flux in the slag.

3. Coal has a tendency to segregate and float with the result thatdanger of over-reduction is avoided. a

4. FeO and T102 being intermittently (or continuously) added'to the bathand slag-fluidity being thereby maintained, equilibrium conditions areunfavorable for. high reduction of titanium.

reduction. The charge therefore melts more The results of these runs aregiven in the folreadily by reason of the higher FeO content at a lowingtable: 1

* Charge, parts I per 190 parts Slag, Per Cent Leach Trivalent Acid to55. Ti Ti Ratio Weight Coal Lime T101 Fe 7 Per cm! Per cent 11: 2 00-120-0 2.1 00.0 15 2.22 14 0 13.0 1.1 2.0 88.5 10 2.10 12 0 10.2 10.0 2.1 v21.5 12 2.20 14 0 10.4 10.0 3.0 80 15 2.20 14 0 11. 1 a. 1 a. 1 s0 10 2.10 .14 0 50.5 0.0 3.1 00.5 13 2.20

1 Uncorrected i01- FeO to Fe1O1.

given temperature. With the initial production of a relatively high FeOslag, there is better opportunity for a homogeneous slag because of theOver-reduction of TiOa is less likely and the slag may be tapped at ahigher iron content with lower trivalent titanium content.

Additional smelting data was obtained from operations conducted in arectangular furnace operated with three-phase power with the threeelectrodes in line. Provision was made for charg= ing along the sidewalls of the furnace by introducing the charge mix through the roof orthrough doors in the end walls. The furnace was operated with batchcharging. The results of II are given in the following table. The weightgain as reported is uncorrected for oxidation of iron, and in order toobtain the weight gain attributable to the oxidation of trivalenttitanium oxide, one-seventh of the per cent of iron (as Fe) in the slagshould be subtracted from the weight gain as reported. The trivalent Ti"is the percentage of solubilized titanium present in the to titaniumdi-' 2 The following series of runs were carried out in a three phaseelectric arc furnace with closely spaced, triangularly disposedelectrodes. The furnace was continuously operated with intermittentcharging on the slag bath at 10 to 30 minute intervals.

Charge, parts per 100 parts Slag, per cent R of ore Y Lefiach Add) un 6-I w t I Ti Ratio Coal Lime T101 r0 39 1a 0 1s 5 3.1 2.1 1a 1 15 5 2.589.5 2.05 K. 13 1 15 5 3.2 00 2.1 L 12 1 10 s 2.8. as 2.2

1 Unconected lor F00 to F0203.

' intermediate in the case of each slag,

solution was that is The trivalent titanium in the leach leach solutionin the form of trivalent titanium. 65 appear to have any virtue initself, it is an index Charge, Parts per Parts Slag, Per Cent Power ofore leach Tflvalmt Acid Run Kilowatts Recov- T to Tl warm 7 Coal LimeT10, Fe Gum Per Cent Per Cent i m 12 2% 68-70 0-10 2 5 00-02 10 2.15 11s00 14 2 10 5-6 21 00-02 10 2.1

In another series of runs, the rectangular threephase are furnace wasintermittently charged.

of the trivalent titanium in the slag. Low iron slags, containing lessthan about 2% iron, are

In both cases fresh charge rolled into the molten slag bath causingthese differences as ous material for the production of of the loweroxides of titanium to be suitable for chemical processing to producepigment titanium dioxide.

Slags containing more than 15% iron generally contain little or notrivalent titanium.

Another advantage resulting from the control of the reduction oftitanium is that the metallic iron product (pig iron) produced is low intitanium. Sulfur enters the iron, and since no soda and relativelylittle lime are used, the phosphorus enters the iron rather than theslag.

The advantages of phosphorus-free titaniferpigment titanium dioxide ofthe rutile type are discussed in the copending application for UnitedStates Letters Patent of Lewis C. Copeland and Clayton W. Farber, Ser.No. 683,150, filed July 12, 1946. In the slag concentrate of theinvention, it is possible to hold the phosphorus content of the slagbelow the critical limit, that is with the ratio of P205 to T10: in theleach solution below 0.00025 (1. e. less than 0.025% P205 on the basisof the 1102). Indian ilmenite ore contains more phosphorus than theother titaniferous ores commonly used for pigment manufacture. A typicalIndian ilmenite ore analyzed 0.17% P205 and 60% T102, giving 9. P205 toTiO: ratio of 0.0028, which is approximately ten times the criticallimit. Tabulated below are the analyses-of titanium slag concentrates inaccordance with the invention obtained by smelting this high phosphorusore:

s] Per Cent Per Cent Per Cent Ratio 'rio, Fe no, moi T10,

from these ores sufliciently low even with iron contents considerablyhigher than the maximum of the preferred range.

Recapitulating the foregoing invention, in addition to its high gradeand good digestibility, contains from to 20% of lime and iron,calculated respectively as CaO and Fe, of which at least 2% is iron.Thus, the slag may contain from 2 up to 20% iron and from 18% down to aninsignificant amount (say around 0.1%) lime. In its preferred form, theslag contains at least 70% titanium calculated as T102, from 4 to ironcalculated as Fe, and up to 14% lime calculated as CaO. Slags of theinvention prepared from ores with extremely low or negligible calciumcontent (0.05% or less CaO), such for example as Petit Pas or ilmenite,without any addition of lime to the smelting charge, will contain onlyan insignificant amount of lime, e. g. 0.1% or less. Since lime is forall practical purposes the only flux deliberately added to the smeltingcharge, the slag contains no sodium oxide or only such insignificantamount as may be present in the ore. Additionally, the slag is nothighly reduced.

The presence of trivalent titanium tends to increase the viscosity ofthe slag. In the smelting operation, formation of trivalent titanium isheld to a minimum by adjusting the quantity of coal included in thecharge so that enough unreduced ferrous oxide is available to form, withthe other slag-forming constituents present,

the slag. The equilibrium between trivalent titanium and ferrous oxideleft in the slag is affected by the amount of lime in the slag eitherfrom the gangue materials or added extraneously as a flux. For example,with 3 or more per cent (based on the ore) of lime added to a typicalore, a slag can be produced several per cent lower in iron withoutexcessive reduced titanium.

Such corrosion may be minimized by so operating the furnace that the newcharge is retained at a temperature below the melting crucible.Thereafter by proper attention to the rate of power input, the rate ofcharging, the depth of bath, and the cooling of the shell, this frozenslag crucible can be maintained indefitemperature or such slags ishigher than that of lower grade slags fiuxed with ferrous oxide and,more particularly, than that of slags fiuxed with lime. Where it isdesirable to produce a slag of lower TiOz grade, either as a directobjective or for the purpose of reducing the operating temperature ofthe furnace, lime may be added as a flux. Lime fluxing may be increaseduntil slags are reduced to about 65% T10: grade without any particulardiificulty. Below'this T10: content, precautions demanded by increasingfluidity of the slag must be observed. Below 60% T10: grade; lime-fiuxedslags are very fluid and corrosive.

/ Fundamentally, the slag concentrate of the invention is obtained by aneconomically satisfactory concentration of titanium-iron ores by partialremoval of iron therefrom. While this concentration is preferablycarried out in an electric furnace, as hereinbefore described, theconcentration has been effected with the production or slags of theinvention in a reverberatory furnace.

We claim:

1. A titanium slag concentrate the constitu-- cuts of which areconfined, with the exception of the possible addition of extraneouslime, to those normally present in ores of titanium and iron and in thecoal used to smelt said ores to produce a metallic iron product and thetitanium slag concentrate capable of being separated from one anotherwhile in the molten state at a temperature of 1500" to 1'700 C., saidslag concentrate containing as the essential components from 2 to 20%iron oxide calculated as Fe, up to 18% lime calculated as CaO, the totalamount of said iron and lime ranging between 5 and 20%, and .the balancetitanium oxide, the minimum titanium oxide content being 60% calculatedas TiOz, said slag concentrate being further characterized in that uponsulfuric acid digestion and leaching at least 85% of the titanium isrecoverable in the reach solution with an acid-to-titanium ratio in thesolution of between 1.8 and 2.3.

2. A titanium slag concentrate the constituents of which are confined,with the exception of the possible addition of extraneous lime, to thosenormally present in ores of titanium and iron and in the coal used tosmelt said ores to produce a metallic iron product and the titanium slagconcentrate capable of being separated from one another while in themolten state at a temperature of 1500 to 1700 C., said slag concentratecontaining as the essential components from 4 to iron oxide calculatedas Fe, up to 14% lime calculated as CaO, the total amount of said ironand lime ranging between 5 and and the balance titanium oxide, theminimum titanium oxide content being 70% calculated as TiOz, said slagconcentrate being further characterized in that upon sulfuric aciddigestion and leaching at least 85% of the titanium is recoverable inthe leach solution with an acid-to-titanium ratio in the solution ofbetween 1.8 and 2.3.

3. A titanium slag concentrate the constituents of which are-confined,with the exception of the possible addition of extraneous lime, to thosenormally present in ores of titanium and iron and in the coal used tosmelt said ores to produce a metallic iron product and the titanium slagconcentrate capable of being separated from one another while in themolten state at a. temperature of 1500" to 1700 C., said slagconcentrate containing as the essential components from 2 to 20% ironoxide calculated as Fe, up to 18% lime calculated as CaO, the totalamount of said iron and lime ranging between 5 and 20%, and the balancetitanium oxide, the minimum titanium oxide content being 60% calculatedas TiO: with part of the titanium present in the form of trivalenttitanium but not exceeding an amount corresponding to a weight gain of3.5% attributable to oxidation of trivalent titanium to titanium dioxideas a result of an oxidizing heat treatment.

4. A titanium slag concentrate the constituents of which are confined,with the exception of the possible addition of extraneous lime, to thosenormally present in ores of titanium and iron and in the coal used tosmelt said ores to produce a metallic iron product and the titanium slagconcentrate capable of being separated from one another while in themolten state at a temperature of 1500 to 1700 C., said slag concentratecontaining as the essential components from 4 to 15% iron oxidecalculated as Fe, up to 14% lime calculated as CaO, the total amount ofsaid iron and lime ranging between 5 and 20%, and the balance titaniumoxide, the minimum titanium oxide content being calculated as T102 withpart of the titanium present in the form of trivalent titanium but notexceeding an amount corresponding to a weight gain of 3.5% attributableto oxidation of trivalent titanium to titanium dioxide as a result of anoxidizing heat treatment.

WILLIS M. PEIRCE. ROBERT K. WARDIG. LUTHER D. FETIEROLF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 625,656 Elbers May 23, 1899921,686 Fitzgerald et al May 18, 1909 930,344 Borchers Aug. 10, 19091,334,004 Van der Toorn Mar. 16, 1920 1,743,885 Gardner et a1 Jan. 14,1930 1,745,360 Desilva et a1. Feb. 4, 1930 1,831,852 Farup Nov. 17, 19312,375,268 Wyckofi May 8, 1945 2,445,377 Wyckofl July 20, 1948 2,471,242Royster May 24, 1949 FOREIGN PATENTS Number Country Date 3,582 GreatBritain 1901 OTHER REFERENCES smelting of Titaniferous Ores in the BlastFurnace, by A. Rossi, published in Iron Age, vol. 57 (1896) pages 3546,464-9.

